File:Glacier Mass Balance Map.png

From Global Warming Art

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Description

Graph of the annual and accumulated changes in average glacier thickness during the last 50 years.

The effective rate of change in glacier thickness, also known as the glaciological mass balance, is a measure of the average change in a glacier's thickness after correcting for density variations associated with the compaction of snow and conversion to ice. The map shows the average annual rate of thinning since 1970 for the 173 glaciers that have been measured at least 5 times between 1970 and 2004 (Dyurgerov and Meier 2005). Larger changes are plotted as larger circles and towards the back.

During this period, 83% of surveyed glaciers showed thinning with an average loss across all glaciers of 0.31 m/yr. The most rapidly growing glacier in the sample is Engabreen glacier in Norway with a thickening of 0.64 m/yr. The most rapidly shrinking was Ivory glacier in New Zealand which was thinning at 2.4 m/yr. Ivory glacier had totally disintegrated by circa 1988 [1].

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This figure was originally prepared by Robert A. Rohde from published data.

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Notes

It should be acknowledged that glacier sampling is heavily biased towards North America and Europe. Substantial unsampled mountain glaciers exist in South America, Asia and the margins of Antarctica. However, the glacier distriution is also not uniform. Africa has only a handful of glaciers and continental Australia has none. Despite their relative importance, none of the marginal Antarctic glaciers have had their mass balance sampled at least 5 times since 1970.

These estimates of ice sheet thinning do not include glacier mass lost due to iceberg calving. Such calving is not significant for most mountain glaciers since only a small proportion of these glaciers terminate in large bodies of water.